The present invention pertains to a self adjusting eccentric pivot mechanism and in particular to a pivot mechanism for a vehicle seat recliner assembly to eliminate backlash in the recliner assembly gears.
In many mechanical applications, motion is transferred from one element to another by rotation of a first element while in contact with a second element. A typical application is a geared system comprising a drive gear and a driven gear. In applications where the output loading is relatively constant, i.e. where the resistance to rotation of the driven gear remains constant, contact is maintained between the drive and driven gears by this output loading. At certain times, however, variable output loading or variable input conditions can cause intermittent loss of contact between the drive and driven gears. This loss of contact can produce undesirable consequences such as variations in the output velocity, uneven wear on the contact surfaces or undesirable noise patterns.
Loss of contact can be due to various reasons such as processing variations in the manufacture of the elements or gears in the system such as the eccentricity of the input or output gears, variations in the distance between input and output gears and variations in the pivot axis location. Typical gearing systems are designed with a small clearance between the engaging gear teeth called backlash to allow for process variations. In some applications this clearance is manually adjusted at assembly to maintain a predetermined clearance without creating binding or excessive wear of the gear teeth.
One example of a gear system is a seat back recliner of a vehicle seat assembly. In many recliner mechanisms, the seat back is carried by a pair of support arms pivotally mounted to the lower seat frame or seat cushion. The support arm, at least on one side of the seat assembly, forms a sector gear portion with a number of gear teeth positioned in an arc about the seat back pivot axis. A pinion gear rotatably carried by the seat frame has teeth meshing with the teeth of the sector gear portion. The seat back is locked in place by a lock mechanism that prevents rotation of the pinion gear. This lock is selectively releasable to allow the pinion gear, and hence the seat back support arm, to both rotate about their respective axes to adjust the reclined position of the seat back.
As is typical with gearing systems, there is backlash present between the teeth of the pinion gear and the teeth of the sector gear portion which allows some movement of the sector gear portion relative to the locked pinion gear. This backlash will allow the seat back of an unoccupied seat assembly to vibrate when the vehicle encounters certain road conditions. The vibration and noise caused by the vibration is amplified by the seat back frame such that at the top of a seat back the movement can be relatively large. The noise and vibration can result in customer concerns and complaints.
One solution to the vibration and noise problem is to provide an eccentric pivot for either the seat back arm or the pinion gear which is used to set the location of the pivot axis of one of the two gears at the time of assembly to provide the minimum backlash necessary for proper operation of the mechanism. While this eliminates excessive backlash, the solution is not a complete solution. Some backlash must remain to prevent binding of the gear teeth. In addition, since the gears themselves may not be concentric, the minimum backlash at one position of the gears may provide excessive backlash at a second position of the gears or may cause binding of the gears.
It is an object of the present invention therefore to provide a self adjusting eccentric pivot to provide a predetermined minimal loading on the gear teeth to maintain proper contact of the sector gear portion teeth with the pinion gear teeth at all times. The gear engaging force must be sufficient to prevent vibration of the seat back during road conditions expected to be encountered by the vehicle.
It is a feature of the self adjusting pivot to enable the pivot axis of one gear to move relative to the other gear throughout the range of motion of the gears to adjust for variations along the circumference of the two gears.
The self adjusting pivot includes a pivot pin with an eccentric member rotatably carried thereon. The eccentric member has an outer periphery that is eccentric relative to the axis of the pivot pin. It is upon this eccentric shoulder that one of the two gear members is rotated. A biasing spring is coupled to the eccentric member to rotate the eccentric member in a direction tending to urge the eccentric axis into a position disposed between the axis of the first pivot and the axis of the other gear such that the two gears are forced toward one another. By forcing the gears together, backlash between the gears is eliminated. Thus, the vibration of the seat back and the noise produced is thereby eliminated. The biasing spring enables the eccentric member to rotate and move the sector gear either toward or away from the pinion gear as the gears are rotated to accommodate variations in the gears themselves to avoid binding.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.